Enhancing Toughness and Microstructural Memory by Coupling Crystallinity, Elasticity, and Plasticity in Layered Materials Composed of Liquid Crystalline Oligomers

Molecular dynamics simulations are
used to show that triblock oligomers,
which are first preassembled into a lamellar phase and then cross-linked,
exhibit high extensibility and toughness in response to uniaxial tensile
deformation parallel to the layer stacking. A coarse-grained model
is adopted based on a coil–rod–coil oligomer capped
with cross-linkable units. Upon uniaxial strain, a buckling instability
ensues in the uncross-linked systems, which eventually leads to defective
lamellar “islands” as the stress drops off. In contrast,
a toughening behavior, manifested as a “sawtooth” stress–strain
profile, is observed in the cross-linked systems, which is associated
with “recrystallization” of the rod domains mediated
by the interlayer bonds formed upon cross-linking. It is also shown
that this toughening mechanism can be encoded in longer multilayer-spanning
oligomer designs that forsake the cross-linking step. These structures,
which integrate rigidity, elasticity, and plasticity, could be leveraged
to experimentally realize novel materials with shape-memory and self-healing
properties.